This invention relates to improvements in mechanical fasteners, and more particularly concerns a mechanical fastener for attaching ablation tiles to the strain isolation pad outer covering of space vehicles while in outer space.
Space vehicles which exit and re-enter the Earth's atmosphere must be protected against the great heat which is generated by such travel. Vehicles such as the Space Shuttle use an outer layer of ceramic tiles attached to an inner layer of strain isolation pad for such protection. Often some of these ceramic tiles are damaged when the space vehicle leaves the Earth's atmosphere. In order to prevent having a vulnerable spot in the vehicle's heat proof covering these damaged tiles must be replaced before the vehicle re-enters the Earth's atmosphere. The present invention provides a convenient method of attaching replacement tiles to the strain isolation pad while the vehicle is in outer space.
The need to replace heat shield tiles on a vehicle in outer space came about only recently when the Space Shuttle was conceived. To date, there has been no standard method for attaching replacement tiles. Adhesives are generally ineffective in outer space because the absence of atmosphere prevents the adhesive from setting. Therefore, a mechanical fastener of some type must be used. Such a mechanical fastener must have sufficient strength to hold the replacement tile in place as the vehicle re-enters the atmosphere. It must also be of the type that facilitates quick, easy installation of replacement tiles by a space-suited astronaut in outer space. The present invention was designed with these constraints in mind.
Existing mechanical fasteners typically require use of a prefabricated socket in the attachment surface which is to receive an insert portion of the fastener. A threaded aperture in an attachment surface which receives a bolt to connect an object to the attachment surface is a simple example of this type fastener. However, a fastener utilizing a prefabricated socket cannot be used to attach a replacement tile to a spacecraft strain isolation pad because it is not known beforehand where the socket will be needed. Therefore a fastener that is capable of attaching a replacement tile directly to a strain isolation pad is needed. Although fasteners of this type do exist, no such existing fastener is entirely suitable for the stated purpose. For example, screws with various type threads are available. However, screws are not adjustable in length and require repeated rotation to fasten. Since replacement tiles might be of various thickness, a fastener which is adjustable in length is desirable. Also, since an astronaut will have to use the fastener while in outer space, the fastener should be one which requires very little manual manipulation. Therefore, a one-piece screw type fastener is not appropriate for the desired use.
It is therefore an object of the invention to provide a mechanical fastener for attaching heat shield tiles to the strain isolation pad of a space vehicle while that vehicle is in outer space.
A further object of this invention is to provide a fastener which is easy to use in outer space and yet is of sufficient strength to hold the replacement heat shield tile to the strain isolation pad as the space vehicle re-enters the Earth's atmosphere.
It is still another object of this invention to provide a fastener that holds the replacement tile tight against the strain isolation pad so as to provide maximum heat protection.
Yet another object of this invention is to provide a fastener which is adjustable in length to allow for variation on tile thickness.